Question

6. (Answer this question using the neutral theory of molecular evolution) One of Charles Darwin's main ideas was that life evolves by natural selection, following a rule of "survival of the fittest." For example, if you look historically at giraffes, it is hypothesized that those with taller necks tended to be selected for evolutionarily because they could reach more food high up in trees. When we consider DNA, the same principles of natural selection apply. Those DNA regions that have a selective advantage survive at the expense of other DNA that is not as successfully adapted. (15 p) a. This is true b. This is false c. This can be true, though most DNA is NOT selected for in a Darwinian way d. This can be true; most DNA *is* selected for in a Darwinian way 7. If you flip (i.e. rotate) an internal node, does the topology of a tree change; do the branch lengths change? (10 p) a. The topology changes. b. The branch lengths change. c. Both the topology and the branch lengths change. d. Neither the topology nor the branch lengths change.

Answer 1

ANSWER 6

Correct answer is c.

This can be true. Though most DNA is not selected in the Darwinian way.

In evolution the DNA of a species undergoes a gradual change over many generations.

One of the ways this happens is natural selection (Darwinian theory) when certain genetic mutations create traits which augment survival of an organism. These mutations are more likely to be passed on to the next generation. For example high altitude adaptation in people of Tibet which allows their blood to carry more oxygen due to a mutation in the gene.

In spite of the ability of an organism to adapt to its environment, natural selection affects only about 8 per cent of our genome.

The neutral theory of molecular evolution states that most evolutionary changes at the molecular level and species variation within a species or between species are due to random genetic drift of mutant alleles that are selectively neutral. The theory assumes that most mutations that are not deleterious are neutral instead of beneficial.

According to the neutral evolution theory, mutations in the rest of the genome may freely change frequency in populations by chance.

It allows the possibility that most mutations are deleterious. But they do not create a significant amount of variation because they are rapidly removed by natural selection.

ANSWER 7

Correct answer is d.

If you rotate the internal node of a tree neither topology nor branch lengths change

A phylogenetic tree is a diagram that represents evolutionary relationships among organisms. They are hypothetical diagrams first proposed by Darwin. He proposed the notion of an evolutionary tree in his book - The origin of species.

It shows the relationship between various evolutionary groups.

The pattern formed by the connecting of branches represents our understanding of how the species in the tree evolved from a series of common ancestors. Every branch point (internal node) represents a divergence event, or splitting apart of a single group into two descendant groups.

Rotating a tree about its branch points using the branch point as a pivot doesn't change the information it carries. It shows the same relationship. Neither the topology nor branch length changes.

This shows that the order of tips on a tree is actually arbitrary. What really matters is the way that the species are connected through their common ancestor